When fluids are transported in a pipeline, it is sometimes desired to inject other fluids into the pipeline. Pipelines rely on pressure to move their contents, and in high pressure pipelines, it can be difficult to inject the fluid. An example of this can be found in the petroleum industry, where, when transporting natural gas by pipeline, one must be concerned with the formation of hydrates in the pipeline, especially in colder climates or in offshore operations. Once the thresholds of temperature and pressure have been crossed, water and certain gas molecules such as methane and ethane, all of which may be found in natural gas, call precipitate from the gas being transported. As a result, the pipeline, valves, or other equipment used in the operation may become less efficient or even blocked. Commonly, liquids such as methanol, glycol or diethylene glycol are mixed with the gas to prevent the formation of hydrates by shifting the thermodynamic hydrate formation to lower temperatures and higher pressures. Other inhibitors that inhibit hydrate formation when present in smaller amounts are also currently being developed. Because of the pressure of the natural gas being transported, the problem is then how to inject the inhibitor into the pipeline.
A common practice in the petroleum industry is to use a diaphragm and plunger apparatus to inject hydrate inhibitors into the pipeline. The injection of the inhibitor is controlled by the plunger. As the plunger moves up, the inhibitor is drawn into a tube by opening a valve due to the reverse pressure created in the tube that connects the tube to a reservoir of the inhibitor. As the plunger moves down, the reservoir valve is closed, and another valve is opened that connects the tube to the pipeline. With the plunger applying more pressure than the pipeline, the valve is opened and the inhibitor is pushed into the pipeline. This process is then repeated. The motion of the plunger is controlled by a diaphragm above it. When the plunger is at its highest point, the diaphragm""s side opposite the plunger is pressurized with gas from the pipeline, forcing it and the plunger downward. The difference in size between the diaphragm and plunger, for example, 10xe2x80x3 and xc2xcxe2x80x3 respectively, allows the plunger to apply a positive pressure on the inhibitor and inject it into the pipeline. Once the plunger reaches its lowest point, it trips a switch that causes the gas used to push the diaphragm downward to be vented. With the pressure released, the diaphragm returns to it original shape, and the plunger with it. This design suffers from a few problems. First, the gas used to pressurize the diaphragm is simply vented into the air, causing waste and pollution. Secondly, the setup is designed to inject a certain amount of inhibitor, and while it is possible to change this, the setup then becomes less efficient.
In a preferred embodiment of the invention, there is provided an injector for injecting fluids into a pipeline, the injector comprising a source of fluid to be injected; a first and a second motor valve, the first motor valve having a larger force constant and being connected to regulate flow between the source of fluid and a displacer tube, the second motor valve having a lesser force constant and being connected to regulate flow between the displacer tube and the pipeline; and a control line connected to the first and second motor valve for controlling the first and second motor valve. The source of fluid may be an overhead storage tank. The control line may be pressurized and depressurized by a valve connected to the pipeline. The valve may be a latching solenoid valve. The latching solenoid valve may pressurize and depressurize the control line according to control signals provided by a control panel, the control panel may comprise a timing apparatus that provides control signals to the latching solenoid valve; and a power source connected to the latching solenoid valve for providing the latching solenoid with power. The pipeline may be used to transport natural gas. The injected fluid may be hydrate inhibitor. The power source may be a battery. The battery may be charged by a photovoltaic converter. The natural gas in the source of fluid may be used to fuel a heater. The timing apparatus may comprise a clock with a sweeping hand; a magnet carried by the second hand; and a plurality of magnetically operated switches, the switches positioned to be activated by sweeping the magnet past the magnetically operated switches. The magnetically operated switches may be reed switches. A plurality of magnets and a plurality of magnetically operated switches may be used to increase the frequency of switching.
In another preferred embodiment of the invention, there is provided a hydrate inhibitor injector for injecting hydrate inhibitor into a natural gas pipeline, the injector comprising a source of hydrate inhibitor; and first and second valves on a line connected to the source of hydrate inhibitor, the valves configured to isolate a slug of hydrate inhibitor in response to a first signal from a controller and deposit the slug of hydrate inhibitor in a natural gas pipeline in response to a second signal from the controller. The source of hydrate inhibitor may be an overhead storage tank. The natural gas in the overhead storage tank may be used to fuel a natural gas heater. The first and second valves may be motor valves with different force constants. The controller may comprise a control line; a valve for pressurizing the control line in response to a first control signal and depressurizing the control line in response to a second control signal; and a power source connected to the valve for providing power to the valve. The valve may be a latching solenoid valve. The first and second control signals may be provided by a timing apparatus comprising a clock with a sweeping hand; a magnet carried by the sweeping hand; and a plurality of magnetically operated switches, the switches positioned to be activated by sweeping the magnet past the magnetically operated switches. The magnetically operated switches may be reed switches.